Motors are widely used not only in home appliances such as washing machines, refrigerators, air-conditioners and vacuum cleaners, but also in electric vehicles and hybrid vehicles, which have recently been receiving attention.
Among them, a permanent magnet motor using a permanent magnet rotates a rotor using a magnetic interaction between a magnetic field of a coil through which an electric current flows and a magnetic field of the permanent magnet.
To drive the permanent magnet motor, a driving apparatus, such as an inverter, which is capable of applying a driving voltage is required. Since the magnetic field generated by the rotor of the permanent magnet motor is determined depending on a location of the rotor, the inverter should apply the driving voltage in consideration of the location of the rotor.
Eventually, in the driving voltage, a phase of the driving voltage is changed according to a rotating speed of the permanent magnet motor, an output torque and the location of the rotor.
As described above, to control the permanent magnet motor, the inverter should apply the driving voltage which is changed according to the rotating speed of the permanent magnet motor, the output torque and the location of the rotor. Therefore, to control two or more permanent magnet motors, two or more inverters that control the motors, respectively, are required.